<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>map</title>
</head>
<body>
	<script type="text/javascript">
		var arr = []
		var testArr = arr.map((value, index, array) => {
			return index // , index, array
		})
		console.log(testArr)

		var users = [
		  {name: "张含韵", "email": "zhang@email.com"},
		  {name: "江一燕",   "email": "jiang@email.com"},
		  {name: "李小璐",  "email": "li@email.com"}
		];

		var emails = users.map(function (user) { return user.email; });
		console.log(emails)
	</script>
</body>
</html>